The project utilizes new diagnostic methods and prototypic treatments in three controlled clinical trials attempting to better characterize the pathophysiology of chronic pain. The first study is a double-blind clinical evaluation of the effect of iontophoretically applied dexamethasone, in comparison to placebo, for temporomandibular joint pain. Subjects determined to have internal derangement of the temporomandibular joint complete a battery of analgesic and psychologic questionnaires prior to drug administration. Mandibular range of motion (including vertical, lateral, and protrusive movements) are assessed and recorded by an associate investigator blind to the treatments. Subjects randomly receive either 0.4% dexamethasone in a vehicle of 4% lidocaine or saline placebo by iontophoretic administration. Following each session, subjects complete analgesic scales and have range of motion measured by an associate investigator. Approximately 50% of the projected sample of 60 subjects have completed the protocol. In the second study, subjects are diagnosed into one of four groups as determined by clinical signs and symptoms:localized masticatory myalgia, fibromyalgia, polymyalgia rheumatica, and normal controls. Each subject undergoes masticatory muscle palpation with a pressure algometer producing uniform and consistent pressure during pre- and post-manipulation examinations. Magnetic resonance spectroscopy (MRS) is also performed and interpreted by a radiologist blind to the diagnoses. After collection of baseline palpation and MRS data, subjects are asked to chew at a rate of approximately 80 chewing strokes per minute in order to stress the masticatory musculature. Palpation and MRS are performed following the exercise in the same manner as the baseline measurements. Differences between groups in exercise tolerance, tissue pH, or phosphate energy metabolism may provide insight into pathophysiologic processes contributing to chronic facial pain of muscular origin. In the third study, patients with suspected neuropathic pain undergo a complete dental, neurologic, and psychiatric evaluation. Magnetic resonance imaging of the brain, mandibular, and maxilla are performed to rule out neoplasm or other detectable pathology. A neurosensory exam is then conducted to localize and identify any sensory deficits which may be contributing to neuropathic pain. Pharmacologic manipulations are also performed on an individual basis in order to further characterize the underlying pathophysiology.